1. Field of the Invention
The present invention relates to a treatment device with a bandage and heater that are essentially planar, yet flexible, and are connected or joined by an attachment device that promotes heat transfer from the heater through the bandage to a wound treatment area where the temperature of tissue is maintained by control of the heater""s operation in a normothermic temperature range.
2. Description of the Related Art
Wounds, in general, are breaks in the integrity of the skin of a patient. A first type of wound may result from mechanical trauma that produces a cut, tear, or an abrasion. There are many instruments of causality for such wounds, including knives, glass, gravel, or a scalpel. A second type of wound may be caused by a combination of heat and pressure wherein the heat alone is insufficient to cause an outright burn. Such wounds include pressure sores, decubitus ulcers, or bed sores, and reflect an injury that is chronic in nature. A wound may also be vascular in origin. In this third type of wound, blood flow through a region may be altered sufficiently to cause secondary weakening of tissues which are eventually disrupted, thus forming a wound. In the case of arterial causes, the primary difficulty is getting oxygenated blood to the affected area. For venous causes, the primary difficulty is fluid congestion in the affected area which backs up, decreasing the flow of oxygenated blood. Because these wounds manifest underlying chronic disease processes, such as atherosclerotic vascular disease, congestive heart failure, and diabetes, these vascular injuries also are chronic in nature, forming wounds with ulcerated bases.
Heat therapy has been used to treat wounds since the days of Hippocrates, with varying results. Up to now, heat therapy for wounds has involved the application of heat under conditions that make the tissues of a wound hyperthermic. Hyperthermic impedes wound healing and may actually damage the wound tissues.
The xe2x80x9cnormalxe2x80x9d range of temperature for the human body is 37xc2x0 C.xc2x11xc2x0 C. (36xc2x0 C.-38xc2x0 C.). This is termed the xe2x80x9cnormothermicxe2x80x9d range. Humans exhibit a thermoregulatory response to core temperature changes as little as xc2x10.1xc2x0 C., wherein xe2x80x9ccorexe2x80x9d as used herein refers to interior portions of the body. This extremely tight temperature control is necessary because virtually all cellular functions, chemical reactions and enzymatic reactions are optimum at normothermia.
Surface tissue varies in temperature according to where on the body it is located. The skin of the torso is usually hypothermic, while the skin of the legs is always hypothermic. The normal skin temperature of the distal leg is approximately 32xc2x0 C., which is considered to be xe2x80x9cmoderately hypothermicxe2x80x9d. The skin temperature of the distal leg of a patient with vascular insufficiency may be as low as 25xc2x0 C., which is xe2x80x9cseverely hypothermicxe2x80x9d. The hypothermic condition of wounds and ulcers inhibits healing. Severely hypothermic skin or wound tissue is in a state that may be termed xe2x80x9csuspended animationxe2x80x9d. In suspended animation, tissue is living, but cellular functions necessary for cell division and collagen deposition are slowed or even stopped. Further, the immune system is inhibited, allowing wounds to become heavily colonized with bacteria. The local application of heat to hypothermic skin will cause some degree of vasodilatation, resulting in an increase in local blood flow. Increased blood flow increases the subcutaneous oxygen tension (PsqO2) which, in turn, increases both collagen deposition and immune function.
Many references report that the immune system is inhibited by hypothermia and activated by mild hyperthermia (fever). Persp Biol Med:439-474, Spring 1980, reports that local body temperature is a critical factor determining host susceptibility, the location of lesions and contracting infectious diseases. New Eng J Med 305:808-814, 1981, reports that animals exposed to cold environments are more susceptible to infectious diseases, whereas exposure to high ambient temperatures often produces a beneficial result. Wound Rep Reg 2:48-56, 1994 and Acta Anaesth Scand 38:201-205, 1994, report that infections caused by a standard inoculum of c. coli or s. aureus were significantly more severe in hypothermic guinea pigs than in normothermic control animals. New Eng J Med 334:1209-1215, 1996, reports that hypothermic colorectal surgical patients had three times more wound infections (19% vs. 6%) than those who were kept normothermic during surgery with a Bair Hugger(copyright) patient warming system described in commonly assigned U.S. Pat. Nos. 5,324,320, 5,300,102 and 5,350,417. Further, six weeks of warming therapy with the Bair Hugger(copyright) patient warming system has successfully healed chronic progressive ulcers which heretofore have been resistant to antibiotic therapies.
As stated hereinabove, enzymatic reactions are promoted by normothermia. Both platelet adhesion and the clotting cascade result from a series of enzymatic chemical reactions. Research efforts have been reported that show hypothermic patients bleeding more than normothermic patients. J Thorac Cardiovasc Surg 104:108-116, 1992, and Ann Surg 205:175-181, 1987, report that skin cooling produces a reversible platelet dysfunction and prolonged bleeding times. Lancet 347 (8997):289-292, 1995, reports that mildly hypothermic total hip arthroplasty patients lost an average of 500 ml more blood and had an 88% higher incidence of transfusion than patients who were kept normothermic with the aforementioned Bair Hugger(copyright) Patient Warming System. Anesthesiology 85: A66, 1996, reports that hypothermic liver transplant patients required twice as many units of blood (18.6 vs. 9.8) and 57% more units of all blood products (46.2 vs. 29.4) than patients who were kept normothermic with the Bair Hugger(copyright) Patient Warming System.
When used to treat wounds; heat has been applied at higher than normothermic temperatures, with the goal of making the wounds mildly hyperthermic. These higher temperatures have often resulted in increasing tissue damage, rather than promoting wound therapy and healing.
Currently available medical devices that apply heat to wounds include infrared lights, warm water pads, warm water bottles, whirlpools and Sitz baths. All types of lesions, such as surgical, chronic, traumatic, donor sites, infected wounds and burns, have been treated with these warming modalities. Particularly difficult has been the application of heat to open wounds such as ulcers. Treatment of a wound with infrared light requires that the wound be positioned under the light during therapy, necessitating patient immobility. Further, the infrared heat causes wounds to dry, thereby slowing the healing process. Warm water pads and bottles and electrical heating pads are cumbersome, reduce patient mobility, and are usually applied to the extremities and held in place with inconvenient wraps such as straps, hook-and-eye material or tabs. Whirlpools and Sitz baths reduce mobility and limit the duration of warming therapy due to skin maceration by the water. None of these modalities is capable of prolonged, uniform, normothermic heat treatment of a wound.
This invention utilizes a heater supported by a structure against tissue and operated by chemical, phase-change, or hot-water means to elevate the temperature of hypothermic skin and subcutaneous tissue of a treatment area to a temperature which is close to normothermic. The invention, in operation, maintains the temperature of such tissue in a normothermic range of about 36xc2x0 C. to 38xc2x0 C.
Preferably, the operation of the wound treatment apparatus is referred to a xe2x80x9cwound treatment areaxe2x80x9d (or xe2x80x9ctreatment areaxe2x80x9d) that may include the wound, unwounded skin adjacent the wound (the periwound), or both.
One purpose of this invention is to raise the wound tissue and/or periwound tissue temperatures toward normothermia to promote a more optimal healing environment. The present invention is not a xe2x80x9cheating therapyxe2x80x9d, per se, where it is the intent of xe2x80x9cheating therapyxe2x80x9d to heat the tissue above normothermia to hyperthermic levels. Rather, the present invention is intended to bring the wound and periwound tissues towards normothermia, without exceeding normothermia.
This invention is also designed to elevate the temperature of the hypothermic skin and subcutaneous tissue of the selected treatment area to a temperature which is close to normothermia. The purpose of this is to create within the wound and periwound tissues of the selected treatment area a more normal physiologic condition, specifically a more normothermic condition, which is conducive to better wound healing. This invention contemplates the use of an active heater to deliver heat to a wound, but the role of the heater can better be described as xe2x80x9cguardingxe2x80x9d against heat loss by providing a heat source to counteract the effects of heat loss.
The concept of a xe2x80x9cguard heaterxe2x80x9d is straightforward. The guard heater is heated to approximately the same temperature as the adjacent heated body. Since heat must flow down a temperature gradient, it can only be lost to a cooler surface. The guard heater is not cooler than the adjacent body and, therefore, cannot accept heat from the adjacent body. The normal temperature gradient for tissue goes from about 37xc2x0 C. deep in the body""s core down to about 32xc2x0 C. at the skin""s surface. With a guard heater in place, heat loss directly from the wound and periwound tissue surfaces is markedly diminished. This decrease in local heat loss provides for the zone of 37xc2x0 C. core temperature to move outward toward the skin, narrowing the gradient from core temperature to surface temperature as the zone of core temperature approaches the surface in the area of the guard heater. The guard heater behaves very much like a perfect insulator, providing a circumstances suitable for warming of the wound with heat flowing from the core. The guard heater of the present invention has an additional advantage over near-perfect passive insulation in that near-perfect insulation would require the use of several inches of bulky insulating material. Such bulkiness in a wound dressing is not practical for proper wound care.
The xe2x80x9cguardxe2x80x9d heater of the present invention, for example, in use on wounds below the knee where vascular insufficiency may occur, operates from above ambient temperature to 38xc2x0 C., which includes the range of xe2x80x9cnormothermiaxe2x80x9d. Obviously, because of the thermal mass of the leg, the blood flow through the leg and inherent inefficiencies of heat transfer, the resulting wound and periwound tissue temperatures usually remain less than the operating temperature of the xe2x80x9cguardxe2x80x9d heater, and probably less than the patient""s core temperature.
In order to deliver normothermic heat therapy to a wound treatment area it would be beneficial to employ standard bandages that are available for wound treatment. In this case, a heater may conveniently be placed on top of a bandage and the heater/bandage apparatus may be placed on the wound treatment area. However it is necessary that the treatment apparatus apply and/or maintain the heat generated by the heater within a normothermic temperature range of about 36xc2x0 to about 38xc2x0 C.
Finally, we have determined that a controller is desirable for operating the heater so that the normothermic heat therapy is implemented at the treatment area.
The present invention enables normothermic heat therapy of wounds by a wound treatment apparatus that includes four components: a thermally conductive bandage, a heater, an attachment device for connecting or joining the bandage and heater, and a controller. The heater is in thermal contact with the bandage over a treatment area and the attachment device maintains the contact. The antecedent attachment device is fashioned so that, during contact, conduction of heat between the heater and the bandage is maximized and, upon removal of the heater from the wound cover, the bandage remains attached to the person""s body. Preferably, the heater and bandage are planar, so as to maintain a low profile for the convenience of the patient, and are flexible, so as to conform to the wound and to the contour of the patient""s body at and near the wound.
The bandage is preferably thermally conductive. Thermally conductive bandages may be made of such materials as hydrogels, hydrocolloids, moist gauze, moist foam, hydrated alginates and polymeric films. In a preferred embodiment, an upper surface of the bandage includes a layer of moisture-impermeable material. With this arrangement, the bandage protects and maintains the humidity of the wound bed and the adjacent tissue.
The heater includes means for generating heat that may take the form of, for example, an electrical resistance element embedded or laminated in a layer of flexible material. The heater may also operate by chemical, phase-change, or hot water means.
The attachment device may be made of a layer of polymeric film with a layer of adhesive applied to both sides which is commonly referred as xe2x80x9ctwo-faced tapexe2x80x9d or xe2x80x9cdouble-sided tapexe2x80x9d. In another embodiment, a layer of adhesive is applied to a surface of the bandage and/or the heater. The attachment device may be continuous across the entire treatment area so that uniform bonding will promote uniform conductive heat transfer from the heater to the bandage. The attachment device employs an adhesive in contrast to straps, hook-and-eye material or tabs. These latter devices allow air spaces to develop between the heater and the bandage resulting in poor and unpredictable heat transfer to the wound.
The controller controls the operation of the heater, maintaining the temperature of the heater in a normothermic temperature range. The controller may maintain such operation on a continuous, or an intermittent basis. Preferably, the controller is programmable, and includes programming or logic to control heater operational parameters including temperature, duty cycle, and therapy cycle.
An object of the present invention is to provide an apparatus for treating a wound by maintaining the temperature of tissue in and/or near the wound in a normothermic range.
Another object is to maintain the temperature of tissue in and/or near the wound in a range of about 36xc2x0 C. to 38xc2x0 C.
A further object is to maintain the temperature of tissue in and/or near the wound in a range of near ambient to about 38xc2x0 C.
Still another object is to provide a low profile, flexible wound treatment apparatus that includes a heater attached to a bandage and a controller connected to the heater for operating the heater so that the apparatus provides a normothermic therapy regime to a wound.
Other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.